Anticoupled amplifier



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March 2, 1943. w. HAGEN ANTI-COUPLED AMPLIFIER Filed May 23, 1940 FigiFiga

Patented Mar. 2, 19143 AN'rIcoUrLEn AMPLIFIER Wolfgang Hagen, Berlin,Germany; vested in the Alien Property Custodian Application May 23,1940, Serial No. 336,777

In Germany April 6, 1 939 3 Claims.

This invention relates to amplifiers in which distortions are obviatedby negative reaction or so-called anti-coupling, and it aims to improvethe function of these devices.

The invention will be understood from the following description and beparticularly pointed out in the appended claims, reference being had tothe accompanying drawing, in which:

Fig. 1 is a diagrammatic view showing a known arrangement; Fig. 2 is adiagram representing one embodiment of the invention; while Fig. 3 is aview similar to Fig. 2 and illustrating a completion of the arrangementthere disclosed.

In all of these figures A denotes an amplifier of any suitableconstruction and whose output resistance is designated Ra. U1 denotes aninput transformer, while U2 designates an output transformer for thisamplifier.

Amplifiers of the kind referred to require the terminal resistances ofthe input and output circuits not to affect the negative reaction, sinceotherwise the amplifiers may be caused to sing in case of varying theterminal circuits thereof. The input circuit vof prior devices is abridge connection of the kind shown in Fig. '1. arrangement comprisesresistances W1, W2, Ws, W4. These, however, must be high enough toprevent the transformer U1 from being attenuated too much. As a resultthe/earth capaci# ties C1, C2 of the transformer, which are indicated bydotted lines, affect the' phase of the negative reaction path,especially in the case of high frequencies. Such undesired changes inphase, however, should as far as `possible be kept out of the negativereaction path, since they can cause the amplifier to sing and can becompensated only by complicated phase networks.

According to the invention, as shown in Fig. 2, transformer U1 comprisestwo symmetrical windings a, b and a, c, loaded with resistances R1, R2.of the two windings. The center point or point of symmetry between theresistances R1, R2 is designated e. These resistances are calculated toprovide for a suitable condition of the input circuit but may be high tosome extent. The reaction current flowing from. d to a passes throughthe windings a, b and a, c in opposite directions. The two currentcomponents thus produced are equal to one another, whereby there will beno reaction voltage arising at winding b, c. The capacity of thewindings of transformer 'Ui is in parallel with the resistances R4, Rs.These, however, are made so low as not to affect the phase of ,thereaction circuit. At Ri This a' is the -center' point or point ofsymmetry the same reaction voltage arises as at Rz. To resistance R1 theamplifier input circuit is connected by high ohmic means (not shown). In

-case such a connection cannot be provided an equivalent simulation ofthe input circuit should be joined in parallel with resistance R2.

This arrangement of the input circuit enables the amplifier to beadjusted simply by varying the negative reaction. Such variation may beeffected by means of resistances Re, Rv, Fig. 3. which constitute apotentiometer effective with respect to the reaction voltage. R7 is alow ohmic resistance. Adjusting this potentiometer causes the degree ofreaction, that is, the amplication, to be regulated in its turn.

While the invention has been described and illustrated in connectionwith two specific embodiments, it is to be understood that variouschanges may be made therein as will occur to those skilled in this art,and that the invention is not limited to the .two forms shown by way ofexample, except as may be required by the claims which follow. I

What is claimed is:

1. An input circuit for a negative feed-'back amplifier, comprising atransformer, a secondary therefor comprising a pair of symmetrical windings connected in series, a pair of loading resistances connected inYseries and shuntedacross the outer terminals of said windings, a circuitto ground connected to the junctiorrpoint of said resistances, a circuitconnecting the terminals of one of said resistances to the input of theamplifier, and a negative feed-back circuit from said amplifierconnected to the junction` point of said windings.

2. An amplifier comprising input and output terminals, an input circuittherefor comprising a transformer, a secondary therefor comprising apair of symmetrical windings connected in series, a pair of loadingresistances connected in series and shunted across the outer terminalsof said windings, a pair of resistances connected in series and shuntedacross the output terminals of said amplier, a feedback circuit;including a resistance, connected between the junction point of the lastmentioned resistances and the junction point of said windings, means forcontrolling the amount of feedback comprising a resistance connectedbetween the junction of said windings and the junction point of saidloading resistances, and circuits connecting the input termifials ofsaid amplifier to opposite terminals of one of said loading resistances.

3. An amplifier comprising input and output terminals, an input circuittherefor comprising a transformer, a secondary therefor comprising apair of symmetrical windings connected in series, a pair of loadingresistances connected in series and shunted across the outer terminalsof said windings, a pair of resistances connected in series and shuntedacross the output terminals of said amplifier, a feed-back circuitincluding a. resistance for regulating the amount of feed-

